In many current wireless cellular systems, the transmit power levels from a mobile unit to a base station of a system are controlled. For example, in some multiple-access systems utilizing a spread spectrum technology, power is controlled at each mobile unit so as to reduce interference caused by the transmissions of one mobile unit upon the transmissions of other mobile units using the same channel. Controlling the transmit power also helps to reduce power at the mobile units, which are generally battery powered. The transmission power of each mobile unit is set high enough such that signals are received at the base station at the desired signal to interference plus noise ratio (SINR), yet low enough to meet the aforementioned goals of interference and power reduction.
To determine the transmission power of each mobile unit, a SINR set point is established for the system. Generally, the SINR set point is based on the minimum data rate required by the system. In wireless communications, the maximum data rate of transmission between two mobile units is directly proportional to the SINR between the two units. A low SINR limits the maximum data rate, because data received with a low signal to noise ratio requires a large amount of processing to extract the transmitted signal from the received waveform. Likewise, a high SINR allows for a high data rate of transmission, because the received waveform requires little processing to extract the transmitted signal. When a system establishes its SINR set point, therefore, the data rate required for proper throughput is determined and a minimum SINR is established to achieve the required data rate. A system SINR set point is then set at or slightly above this minimum SINR. In many systems, the set point of the system is modified over time to account for changes in the number of users in the system and/or environmental phenomena.
Once the SINR set point is determined, the transmit power level for each mobile unit can be established so that a signal sent from a mobile unit is received by the base station at the SINR set point. This is generally accomplished through feedback from the base station to each mobile unit regarding that mobile units received SINR. For example, when a mobile unit transmits a signal to the base station, the base station measures the SINR of the signal and either notifies the mobile unit of its SINR or directly commands adjustment of transmission power of the mobile unit. Either way the mobile unit will set its transmission power such that signals are received at the SINR set point. Since different mobile units may transmit at differing distances from the base station, different mobile units may transmit at different power levels to achieve the SINR set point.
In general, each mobile unit transmits at the minimum power level needed to achieve the SINR set point. This minimizes the amount of interference caused by each mobile unit upon signals of other mobile units. Additionally, when transmitting at the minimum power level, users of the mobile units obtain the maximum talk time from their battery powered mobile units.
Although these current systems succeed in reducing interference and power consumption, these systems cause inefficiencies in network operations, because they are designed to reduce cost and increase simplicity of the system rather than to maximize performance. For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a method for increasing the performance of a wireless network.